P J O Teubner

Electron-impact excitation of Rydberg and valence electronic states of nitric oxide: I. Differential cross sections

Integral cross sections (ICSs) for the excitation of 18 excited electronic states, and four composite excited electronic states, in nitric oxide (NO) have been determined for incident electron energies of 15, 20, 30, 40 and 50 eV. These ICSs were derived by extrapolating the respective measured differential cross sections (M J Brunger et al 2000 J. Phys. B: At. Mol. Opt. Phys. 33 783) to 0° and 180° and by performing the appropriate integration. Comparison of the present ICSs with the results of those determined in earlier optical emission measurements, and from theoretical calculations is made. At each incident energy considered, the current ICSs are also summed along with the corresponding elastic and rovibrational excitation ICSs from B Mojarrabi et al (1995 J. Phys. B: At. Mol. Opt. Phys. 28 487) and the ionization cross sections from Rapp and Englander-Golden (1965 J. Chem. Phys. 43 1464), to derive an estimate of the grand total cross sections (GTSs) for e- + NO scattering. The GTSs derived in this manner are compared with the results from independent linear transmission experiments and are found to be entirely consistent with them. The present excited electronic state ICS, and those for elastic and rovibrational excitation from Mojarrabi et al , appear to represent the first set of self-consistent cross sections for electron impact scattering from NO.

Cross sections and oscillator strengths for electron-impact excitation of the à 1B1 electronic state of water

The authors report absolute differential and integral cross section measurements for electron-impact excitation of the A (1)B(1) electronic state of water. This is an important channel for the production of the OH (X (2)Pi) radical, as well as for understanding the origin of the atmospheric Meinel [Astrophys. J. 111, 555 (1950)] bands. The incident energy range of our measurements is 20-200 eV, while the angular range of the differential cross section data is 3.5 degrees -90 degrees . This is the first time such data are reported in the literature and, where possible, comparison to existing theoretical work, and new scaled Born cross sections calculated as a part of the current study, is made. The scaled Born cross sections are in good agreement with the integral cross sections deduced from the experimental differential cross sections. In addition they report (experimental) generalized oscillator strength data at the incident energies of 100 and 200 eV. These data are used to derive a value for the optical oscillator strength which is found to be in excellent agreement with that from an earlier dipole (e,e) experiment and an earlier photoabsorption experiment.

Sub-Doppler bandwidth atomic optical filter.

We demonstrate what is to our knowledge the first atomic optical filter that uses velocity selection to achieve a passband width that is less than the Doppler width of the filtering transition. A narrow-linewidth pump laser is used to induce circular birefringence in a narrow velocity class of atoms in a dense potassium vapor for 694-nm light resonant with the 4P(3/2)-6S(1/2) transition. The filter displays a single 170-MHz passband at a peak transmittance of 9.5%. The bandwidth is an order of magnitude lower than that of previously demonstrated atomic optical filters.

Nitric oxide excited under auroral conditions: Excited state densities and band emissions

Electron impact excitation of vibrational levels in the ground electronic state and nine excited electronic states in NO has been simulated for an IBC II aurora (i.e., ∼10 kR in 3914 A radiation) in order to predict NO excited state number densities and band emission intensities. New integral electron impact excitation cross sections for NO were combined with a measured IBC II auroral secondary electron distribution, and the vibrational populations of 10 NO electronic states were determined under conditions of statistical equilibrium. This model predicts an extended vibrational distribution in the NO ground electronic state produced by radiative cascade from the seven higher-lying doublet excited electronic states populated by electron impact. In addition to significant energy storage in vibrational excitation of the ground electronic state, both the a 4Π and L2 Φ excited electronic states are predicted to have relatively high number densities because they are only weakly connected to lower electronic states by radiative decay. Fundamental mode radiative transitions involving the lowest nine excited vibrational levels in the ground electronic state are predicted to produce infrared (IR) radiation from 5.33 to 6.05 μm with greater intensity than any single NO electronic emission band. Fundamental mode radiative transitions within the a 4Π electronic state, in the 10.08–11.37 μm region, are predicted to have IR intensities comparable to individual electronic emission bands in the Heath and e band systems. Results from this model quantitatively predict the vibrational quantum number dependence of the NO IR measurements of Espy et al. [1988].

Electron collisions with NO: elastic scattering and rovibrational (0 to 1, 2, 3, 4) excitation cross sections

The relative flow technique, utilizing helium as a cross section standard, has been applied to measure absolute elastic differential cross sections for electron scattering from nitric oxide (NO). The present elastic measurements were conducted at nine energies in the range 1.5-40 eV, which represents an important extension to the only previous study of this system by Kubo and co-workers (1981). Furthermore, the uncertainties in the present data are significantly reduced in comparison to those quoted in the earlier work. The current elastic differential cross sections were measured at the Australian National University over an angular range 10 degrees -130 degrees . We also report the first measurements of absolute differential cross sections for rovibrational (0 to 1, 2, 3, 4) excitation of the NO ground electronic state. These were conducted at six energies in the range 7.5-40 eV and were measured at Flinders University over the angular range 10 degrees -90 degrees . The differential cross sections for both the elastic and inelastic processes are compared with the results of the recent Born-closure Schwinger variational method calculation of Mu-Tao Lee and colleagues (1992).

(e,2e) Spectroscopy of methane

Abstract Measurements are reported on the spectroscopy of methane using the symmetric (e,2e) technique at energies of 600 eV and 1200 eV. The angular correlations of the states with separation energies of 14.2 and 23.1 eV have been measured and compared with the orbital wavefunctions of Snyder and Basch and with some earlier data at 400eV. The angular correlation of the configuration interaction state at 31 eV shows that this state definetely results from the removal of an electron in the 2a 1 orbital. Other structure at high separation energy is also identified with this orbital. Relative strengths of the It 2 and 2a 1 states are compared and found to be in agreement with the theory at 1200eV.

Excitation functions for the formation of metastable He and Ar by electron impact

The authors report the measurement of the electron impact excitation functions from threshold to 200 eV, for the formation of metastable helium and argon, using the time of flight technique. Both excitation functions have a broad maximum approximately 10 eV above threshold. Near threshold the results are in excellent agreement with earlier measurements, but they are in serious disagreement with the results of Kuprianov, the only previous measurements available over a large energy range. Recent plane and distorted wave Born approximation calculations for argon give a poor representation of the data.

Elastic Electron Scattering from CO2

We present measurements of absolute cross sections for low- and intermediate-energy elastic electron scattering from , which have been measured independently on different experimental apparatus in two laboratories. The results are compared with a number of previous measurements and calculations. Whilst there are some interesting differences between recent experimental determinations, the largest discrepancies are observed between experiment and contemporary scattering theory at very low energies.

Absolute differential cross sections for electron impact excitation of the 10.8-11.5 eV energy-loss states of CO2

Absolute differential cross sections (DCSs) for electron impact excitation of electronic states of CO2 in the 10.8-11.5 eV energy-loss range are reported. These data were obtained at the incident electron energies 20,30,60,100 and 200 eV and over the scattered electron angular range 3.5°-90°. The accuracy of our experimental methods has been established independently by using several different normalization techniques at both Sophia and Flinders Universities. Generalized oscillator strengths were derived from our measured DCSs and then extrapolated to zero momentum transfer, in order to determine the optical oscillator strengths. These optical oscillator strengths, where possible, are compared with the results from previous measurements and calculations.

(e, 2e) spectroscopy of N2—valence momentum distributions and configuration interaction

Abstract The noncoplanar symmetric ( e , 2 e ) reaction has been applied to N 2 at 1200, 600 and 400 eV. Separation energy spectra are obtained in the valence region, the observed structure extending to above 60 eV. Electron momentum profiles are measured at a number of separation energies. They agree very well with the momentum distributions for valence orbitals given by SCF calculations. Considerable configuration interaction structure is observed, being primarily due to configuration interaction in the 2σ g hole state. At 1200 eV the spectroscopic sum rule is satisfied within experimental error, confirming the validity of the analysis.